Of the cases belonging to the Indo-European language, Greek has lost the free use of three: instrumental, locative, and ablative. A few of the forms of these cases have been preserved (341, 1449, 1535); the syntactical functions of the instrumental and locative were taken over by the dative; those of the ablative by the genitive. The genitive and dative cases are therefore composite or mixed cases.
N.—The reasons that led to the formation of composite cases are either (1) formal or (2) functional. Thus (1) χώρᾳ is both dat. and loc.; λόγοις represents the instr. λόγοις and the loc. λόγοισι; in consonantal stems both ablative and genitive ended in -ος; (2) verbs of ruling may take either the dat. or the loc., hence the latter case would be absorbed by the former; furthermore the use of prepositions especially with loc. and instr. was attended by a certain indifference as regards the form of the case.